The human ear is composed of the outer ear, including the pinna, the middle ear and the inner ear. The function of the pinna is to guide sound into the ear canal of the outer ear, which further guides the sound from the ear canal of the outer ear via the middle ear to the inner ear. Different kind of hearing devices for compensating for a hearing loss exist and the hearing devices are adapted to be worn in any known way. This may include i) arranging a unit of the hearing device behind the ear with a tube leading air-borne acoustic signals into the ear canal or with a receiver/loudspeaker/speaker arranged close to or in the ear canal such as in a Behind-the-Ear type hearing aid, and/or ii) arranging the hearing device entirely or partly in the pinna and/or in the ear canal of the user, such as in an In-the-Ear type hearing aid or In-the-Canal/Completely-in-Canal type hearing aid.
In general, any type of hearing device is exposed to various internal or external environmental substances that might influence the sound quality of the hearing device, if coming into contact with sound sensitive components of the hearing device. Especially, the internal and external surfaces of the hearing device and the components thereof may be exposed to dirt, moisture, earwax and other damaging substances that might cause an obstruction in the sound path of the hearing device. Thus, hearing devices should survive a harsh environment during daily use.
Generally, the outer ear of the human ear has an oval cross section. When inserting a hearing device into the ear canal it will often be exposed to cerumen, also known as earwax, which build up within the ear canal of the outer ear. The oily substances of earwax tend to migrate on the external and/or internal surfaces of the hearing device, and might potentially penetrate further into the components of the hearing device. On the interior surfaces, the earwax could cause damage to the sound sensitive elements, such as the microphones, receiver, speaker or other internal components, if the sensitive parts inside these internal components is contaminated. Therefore, a reliable protection system is critical for the reliability of the hearing device. Earwax ingress is one of the most common reasons for non-working hearing devices send back to the manufacture for service/repair.
On the external sides of the hearing instrument, such as the behind-the-ear part, the surfaces may further be exposed to dirt, sweat or other potentially damaging substances, which might also migrate into the inner structures of the hearing aid. Thus, it is desirable to protect the sound sensitive parts of the internal components, such as the microphone(s) and/or receivers (i.e. speakers(s)) of the hearing device, against migration of damaging substances from the interior and/or exterior environment that may potentially obstruct the sound conduction path in the hearing device.
Conventionally available earwax, moisture and dirt protection systems use a woven/non-woven filter or substrate placed somewhere in the sound path1—from the outside of the instrument to the microphone. These filters allow sound to pass while the obstructing substances is absorbed in the filter/substrate material. One problem with this kind of protection system is that the filters need replacement on regular basis, to prevent the filters from clogging and block the sound path in the hearing device (e.g. a hearing aid). Many hearing device users find it difficult to replace such filters and might not follow the prescribed replacement intervals and ends up with a non-working hearing device.
Therefore, there is a need to provide a solution that addresses at least some of the above-mentioned.